This invention relates generally to a filter for liquids such as lubricating oil, hydraulic fluid and the like. More specifically, the invention relates to a so-called spin-on filter adapted to thread onto a mounting adaptor of, for example, a hydraulic system or a lubrication system.
A spin-on filter is designed for a specified service life. The filter is then discarded and replaced with a new filter. Typically, more than one manufacturer produces filters which are interchangeable. As a disposable or throw-away type of item, the decision to purchase one brand of filter over a different brand is often based substantially on the price of the filter.
A spin-on filter typically includes a filter element and a seal which are located in a sheet metal canister having an open end. The seal operates to separate the filtered oil from the contaminated oil inside the canister. A baseplate assembly which is adapted to screw onto the mounting adaptor is secured to the open end of the canister by seaming a flange on the baseplate assembly with a flange on the canister. In addition, a helical compression spring normally is located inside the canister of prior filters, between the closed end of the canister and the end of the filter element to hold the filter element in place and, in some instances, to preload the seal.
The presence of the compression spring in the prior filter complicates the assembly of the filter. After the internal components of the filter are assembled into the canister and before the baseplate assembly and the canister have been seamed together, the spring is in a relaxed state and causes the flange of the baseplate assembly to be raised up and substantially separated from the flange on the canister. To insure proper interlocking of the flanges, the spring must be held in compression during the seaming operation. The purpose of the spring is to maintain the filter element and the seal in alignment with the baseplate assembly and in a secured position in the canister.